The measurements of normal acetabular index and Sharp acetabular angle in Chinese hips

Objective To define the normal reference values of acetabular index and Sharp angle through 2333 standard anterior-posterior pelvic radiographs. Methods In our study, 2333 normal anteriorposterior pelvic radiograph images with standard exposure were selected. All the images were diagnozed normal by two radiologists and two pediatricians according to the criteria of T(o)nnis. All subjects were without any neuromuscular diseases and congenital defoemity. The acetabular index was measure in the subjects between age 0 to 10 years, and the groups were divided monthly within 1 year and yearly between 1 to 10years. The Sharp angle was measure in the subjects after 10 years, and the groups were divided yearly in adolescence and decadely in adults. Normal values of each age groups and the correlation charts were completed according to statistical analysis. Results The mean acetabular index was 28.39° in neonates followed by a steep decrease in the first three months after born. It decreased to 22.17°in the 1st year, 12.80°in the 10th years and then kept constant. Acetabular index of the female was generally 1°-2°larger than that of the male with statistical significance. The mean Sharp angle was 46.72°in the 10th years, which decreased to 39.10°in the 18th years and 35.69°in elderly people. Another declination was observed after age 40.Generally no gender difference was observed. Conclusion Acetabular index and Sharp angle vary with age.They reflect a dramatic morphological change in the acetabulum before adulthood and stay constant afterwards. Gender difference is obvious in many age groups but not all. Normal reference ranges of both gender at all age groups should be considered in clinical evaluation. Key words: Acetabulum; X-ray film; Reference values